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Whack-a-Mole Game 

Make] Projects 

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build, hack, tweak, share, discover,- 

Whack-a-Mole Game 

Written By: Steve Hobley 



Blocks (1) 

for clamping PC boards together while 


Clamps (1) 

for clamping PC boards together while 


Computer (1) 

compatible with laser printer. 

Drill bit (1) 

Hand drill (1) 
or Dremel. 

Iron (1) 

Laser printer (1) 

Multimeter with continuity checker 
function (1) 

Soldering iron (1) 

Wire stripper/crimper (1) 

Hookup wire (1) 
from RadioShack 

LM556 IC (6) 
from RadioShack. 

Diodes (11) 
from RadioShack. 

NPN Transistor (2) 
from RadioShack. There are 15 
transistors in each pack. You need 2 for 
30 transistors total. 

PNP Transistor (2) 
from RadioShack. There are 15 
transistors in each pack. You need 2 
packs for 30 transistors total. 

Copper Clad PC board (2) 
4 1/2" x 6 1/8". 

from RadioShack. 

Speaker (1) 
from RadioShack. 

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Whack-a-Mole Game 

Electrolytic Capacitor 1 .0 F (3) 
from RadioShack. 

Electrolytic capacitor 100uF (2) 
from RadioShack. 

Polyester Capacitor 0.1 |iF (1) 
from RadioShack. 

Electrolytic Capacitor 10|iF (10) 
from RadioShack. 

LED. Green (1) 
from RadioShack. 

LED. Red (9) 
from RadioShack. 

Resistor (1) 
from RadioShack 

DIP sockets (6) 

Optional. From RadioShack 

Batteries (3) 
from RadioShack. 

Battery Holder 3XAAA (1) 
from RadioShack. 

Spray adhesive (1) 


Jim Chen designed an excellent electronic "Whack-a-Mole" game using 555 timers, LEDs, 
and bent-diode touch sensors, that you can build on a solderless breadboard; for a full 
explanation, check out his website here . This project is a more permanent version of Chen's 
game, built on a custom PCB. 

Check out more Weekend Projects . 

© Make Projects 

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Whack-a-Mole Game 

Step 1 — Make the PCB 

• I used EagleCAD to lay out the circuit and PCB design for this project. Download and 
install the free version of Eagle CAD here: 

• Download the project design files here: ( schematic and PCB ). To make a board, you can 
either send the PCB files out to a fabrication house, or (if you're feeling brave) etch your 
own board, as follows in this step. 

• Launch EagleCAD and open the project design files, linked above. Print each PCB layout 
layer onto a transparency sheet. The CAD files are the best guide to component placement 
and orientation, so you will also refer to them later. 

• For each of the two layers, use the toner transfer method to transfer the etching mask to 
the copper cladding with an electric iron. Here's a good page on the technique. 

• With the laser toner mask stuck tight onto the copper, etch the rest of the copper away 
with etching solution. Follow this guide: Cheap. Friendly, and Precise PCB Etching as a 
quick circuit board etching method, substituting etching solution for the peroxide, vinegar, 
and salt mixture described. 

• To make your circuit board double-sided, glue the two single-sided boards together back to 
back, using the two drill holes as an alignment reference. I used 3M #77 spray adhesive to 
bond the boards and left them in a press overnight. 

• Print out and iron the label layer onto the top of the board, using the toner transfer method. 
Finally, drill out all the board's through-holes using a 0.75mm drill bit. 

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Whack-a-Mole Game 

Step 2 — Add the Components 

Discharge 1 f 

Threshold 2 L 

Conlrol Voltage J L 

Ou!|*J[ 5 Q 

Trigger $ C 

GND 7 C 


D 14 Vcc 

J 13 DiSCftarfla 

] 12 TTwasftoW 

] 11 GonLrol Voltage 

] 14 RflMt 

J 3 CMpul 

] B Tfigger 

• Connect all the vias on your etched board, the through-hole connections between the 
layers. Locate them by referring to the "vias" layer in EagleCAD. Lace each via hole with 
bare stripped solid wire, then solder the wire front and back, and trim. 

• Add six 14-pin chip holders. This is an optional step, but I prefer to install chips in sockets, 
for easy removal later. 

• The 556 chip contains two 555 timers, one on each side of the chip. 

• The EagleCAD files should make it fairly clear where to place all the components. Work 
slowly and methodically, and you should be fine. 

• Since this board does not have plated through-holes, be sure to place all components high 
on the board. This lets you solder the top and bottom sides of each. 

• Add the nine 150Q resistors. (Brown-Green-Brown-Gold). 

© Make Projects 

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Whack-a-Mole Game 

Step 3 — Add the Components (continued) 

• Add the 10 F capacitors. You can mix and match different capacitor values if needed (as 
I did) if you do not have 10 identical. 

• Add the nine red LEDs. LEDs are polarity-sensitive, so make sure to place them all with 
their flat edge facing "up" on the board (toward the top of the board when it's oriented for 
you to read the printing). 

• Attach the 9 diodes - either 1N4148 or 1N914 diodes will work. These components are 
polarity-sensitive also, so they must be installed in the orientation shown here. Connect 
them with one wire lead (the cathode) looping high over the top, as shown — these wires 
will be our touch sensors. 

© Make Projects 

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Whack-a-Mole Game 

Step 4 — Add the Components (continued) 

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• Now it's time to add the transistors. First up are the NPN type - I've painted these white to 
differentiate them from the PNP kind. 


• Warning: The PNP transistors I used, from a 15 pack, had a non-standard 
pinout that is backwards from that of most PNP transistors (check the 
picture). Be sure to confirm the correct transistor orientation for the circuit. 

• I unfortunately placed all the transistors according the orientation labeled in my CAD 
layout. This was wrong, so I had to pull them all out later, and reorient them with their flat 
sides facing opposite the way they are labelled on the PCB. 

• (I kept muttering "backwards, backwards, backwards..." while doing it (along with a few 
other choice words!! :-)) 

• So if your transistors have their emitter and collector pins arranged the opposite 
way from the ones here, you will need to orient them the other way from these 


© Make Projects 

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Whack-a-Mole Game 

Step 5 — Add the Components (continued) 

• Add the remaining resistors as 

• 220Q Red- Red- Brown 

• 4.7kQ Yellow- Violet- Red 

• 1MQ Brown-Black-Green 

• 100KQ Brown-Black- Yellow 

• 10KQ Brown-Black-Orange 

• 150KQ Brown-Green- Yellow 

Step 6 — Add the Components, Resistors (continued) 

• 220KQ Red Red Yellow 

• 15KQ Brown Green Orange 

• 56KQ Green Blue Orange 

• 22Q Red Red Black 

• Whew! Then after all of that, we 
can add the remaining 10 F, 1 F 
0.1 F, 100 F capacitors, 2 
diodes, battery pack, and the 

• (I almost forgot - pop the 556 chips 
into the sockets, too!) 

• Done! Give yourself a pat on the 
back if you've gotten this far; you 
deserve it! 

© Make Projects 

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Whack-a-Mole Game 

Step 7 — Test Everything 

• "Testing, testing, 1, 2, 3..." You 
should now be able to connect the 
5V power and switch it on. 

• All the lights should come on, and 
you should hear a "BUUUZZZZ!" 
sound, indicating the end of a 
game, from the speaker. 

• To start a new game, touch the 
touch sensors to clear all the 
LEDs. Try to turn off the LEDs as 
they randomly light up for as long 
as you can. If you take too long, 
the buzzer will sound and all of the 
lights will come on at once. 

■ If things are not working 
correctly, check all the 
connections. Use a multimeter 
with a continuity function to 
confirm that all of the solder 
joints are healthy, and the 
connections are sound. 

• Note - in this picture the 
PNP transistors are oriented 

• Check out the YouTube video of 
our 555-Based Whack-A-Mole 
game in action . 

In this age of the microprocessor, it's refreshing to see how one can implement a complex 
"program" using traditional analog circuits. Although this is not a beginner's project, it teaches 
some great fundamental circuit theory to those brave enough to take up the challenge of building 

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Whack-a-Mole Game 

it! In the process, you can also learn a handy electronics skill: etching your own circuit boards! If 
you do build it, we'd love to hear from you. Leave a comment! 

This document was last generated on 201 2-1 0-31 11 :28:1 1 AM. 

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